bundle2: make ValueError messages native strings

mercurial/bundle2.py

@@ -614,9 +614,9 b' class bundle20(object):'
     def addparam(self, name, value=None):
         """add a stream level parameter"""
         if not name:
-            raise ValueError('empty parameter name')
+            raise ValueError(r'empty parameter name')
         if name[0] not in pycompat.bytestr(string.ascii_letters):
-            raise ValueError('non letter first character: %s' % name)
+            raise ValueError(r'non letter first character: %s' % name)
         self._params.append((name, value))
 
     def addpart(self, part):